The first generation of optical fiber systems in the public telephone network used proprietary architectures, equipment line codes, multiplexing formats, and maintenance procedures. This diversity complicated the task of the regional Bell operating companies (“RBOCs”) and the interexchange carriers (e.g., AT&T, Sprint, MCI, etc.) who needed to interface their equipment with these diverse systems.
To ease this task, Bellcore initiated an effort to establish a standard for connecting one optical fiber system to another. That standard is officially named the Synchronous Optical Network, but it is more commonly called “SONET.” The international version of the domestic SONET/SDH standard is officially named the Synchronous Digital Hierarchy, but it is more commonly called “SDH.”
Although differences exist between SONET/SDH and SDH, those differences are mostly in terminology. In most respects, the two standards are the same and, therefore, virtually all equipment that complies with either the SONET/SDH standard or the SDH standard also complies with the other. Therefore, for the purposes of this specification, the SONET/SDH standard and the SDH standard shall be considered interchangeable and the acronym/initialism “SONET/SDH” shall be defined as either the Synchronous Optical Network standard or the Synchronous Digital Hierarchy standard, or both.
SONET/SDH traffic comprises fixed-length packets called “frames” that have a data portion and an overhead portion. The data portion contains the end-user's payload data and is the reason that the traffic exists. In contrast, the overhead portion contains information that describes how the frame should be handled by the network, provides status on the physical connection, and/or enables enhanced out-of-band features.
A node receives traffic at an input port and transmits traffic via an output port. To switch traffic between one or more input ports and one or more output ports, the node must perform the following tasks:                1. each input port must segregate the incoming traffic it receives into individual frames (this is called “deframing”),        2. each input port must extract the data portion and the overhead portion from each frame,        3. each output port must generate new output overhead portions for each frame,        4. a switch in the node must route each data portion to the appropriate output port, and        5. each output port must generate output frames from the switched data portions and the output overhead portions (this is called “framing”).        
In the prior art, these tasks are performed concurrently by one or more input ports and one or more output ports.
FIG. 1 depicts a block diagram of the salient components of telecommunication network 100, which is a SONET/SDH mesh network comprising eight nodes, nodes 110-1 through 110-8, which are interconnected by twenty-two unidirectional links 120 wherein the link denoted 120-a-b transports traffic from node 110-a to node 110-b. Each link arriving at a node comprises one or more input ports, and each outgoing link comprises one or more output ports.
FIG. 2 depicts an exemplary signal 200 transmitted in the network. Signal 200 is composed of fixed-size frames 210-w, where w is a positive integer; furthermore, as shown in FIG. 3, each individual frame 210-w is made up of an overhead portion 310-w and a data portion 320-w. As is well-understood in the art, the overhead portion contains information describing how the frame should be handled by nodes receiving the frame. Also, as is well understood in the art, the overhead and data portions of the frame are not necessarily spatially or temporally contiguous; for example, overhead portions in SONET/SDH frames are interleaved.
As is shown in FIG. 4, overhead portion 310-w comprises one or more overhead blocks 410-w-h, where h is a positive integer, and each of these overhead blocks further comprises one or more overhead cells 420-w-h-m, where m is a positive integer. In SONET/SDH-based networks, overhead blocks correspond to the rows of the overhead portion, and overhead cells correspond to individual bytes (e.g., S1, J0, etc.). As is well understood in the art, the structure of overhead portion 310-w depicted in FIG. 4 can also apply for network protocols other than SONET/SDH.
FIG. 5 depicts a block diagram of the salient components of the architecture of an exemplary node 110-i in network 100 according to the prior art. Node 110-i comprises M input processors 510-1 through 510-M (one for each input port), switch 530, and N output processors 550-1 through 550-N (one for each output port), interconnected as shown.
Node 110-i has M input ports, corresponding to incoming links {120-j1-i, 120-j2-i, . . . , 120-jM-i}, for receiving input signals, where each link 120-jα-i originates from node 110-jα. Node 110-i has N output ports, corresponding to outgoing links {120-i-k1, 120-i-k2, . . . , 120-i-kN}, for transmitting output signals, where each link 120-i-kα terminates at node 110-kα.
Each input processor 510-m segregates its respective incoming data stream into frames and segregates the data and overhead portions of each frame.
Switch 530 switches the data portions, as is well understood in the art.
Each output processor 550-n: 
(1) receives the switched data portions from switch 530,
(2) generates a new output overhead portion for each data portion,
(3) assembles the data and output overhead portions into output frames, and
(4) transmits the output frame on output port 120-i-n, as is well-understood in the art.
Note that in SONET/SDH-based networks M typically equals N at every node; however, in other types of networks it may be possible to have nodes with M≠N. Additionally, each node has a plurality of input ports and/or a plurality of output ports; thus N+M>2.